I have recently noticed that my '87 W124 runs rough in rainly days, can that be my imagination? The car idles very rough and smooths out somewhat if I put it in neutral. What can be the cause of it and what I should do to fix it? It has not been tune up since I bought it last August. The previous owner had the tune up done before he sold the car to me and I have the service record on what was done. The car has over 260K miles on the clock. Any help is appreicated.

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95 R129
04 Infiniti G35.5 BS
10 X204